UNIVERSIDADE DE BRASÍLIA - INSTITUTO DE GEOCIÊNCIAS
TESES DE DOUTORADO
EM GEOCIÊNCIAS SOBRE REGIÕES BRASILEIRAS
José Oswaldo de Araújo FilhoCARACTERÍSTICAS ESTRUTURAIS E EVOLUÇÃO TECTÔNICA DA SINTAXIS DOS PIRINEUS, BRASIL CENTRAL
Palavras-chave: sintaxis, cinturões fold-thrust, Orogenia Brasiliana, colagem do Gondwana, zones de cisalhamento
UNIVERSITY OF ILLINOIS,Urbana- Champaign, Illinois, USA
Tese de Doutorado defendida em 8/12/1998
Orientador: Stephen Marshak,University of Illinois
Banca: Bruce Faulke, University of Illinois; Albert T. Hsu, University of
Illinois, and University of California at Berkeley; Thomas F. Anderson,
University of Illinois.
RESUMO
UNIVERSITY OF BRASÍLIA - INSTITUTE OF GEOSCIENCES
PhD THESES ON EARTH SCIENCES OF
BRAZILIAN REGIONS
José Oswaldo de Araújo Filho
oswaldo@unb.br
STRUCTURAL CHARACTERISTICS AND TECTONIC EVOLUTION OF THE PIRINEUS SYNTAXIS, CENTRAL BRAZIL
Key words: syntaxis, fold-thrust belts, Brasiliano orogeny, assembly of Gondwana, shear-zones
UNIVERSITY OF ILLINOIS,Urbana- Champaign, Illinois, USA
DATE OF ORAL PRESENTATION: 8/12/1998
ADVISOR: Stephen Marshak,University of Illinois
Committe: Bruce Faulke, University of Illinois; Albert T. Hsu, University of
Illinois, and University of California at Berkeley; Thomas F. Anderson,
University of Illinois.
ABSTRACT
The Pirineus Syntaxis is a pronounced-to-the-foreland curve in the otherwise north-south trending strutural grain of the Brasilia Orogenic belt, along the western margin of the São Francisco craton in central Brazil. Deformation in the Brasília belt has been attributed broadly to the Neoproterozoic Brasiliano (=Pan-African) orogeny. My 1:50,000-scale mapping of 12,000 km2 encompassing the Pirineus syntaxis suggests that the curve represents the overlap of two distinct fold-thrust belts.The southern limb of syntaxis consists of an east-verging fold-thrust belt in which spoon-shaped thrust sheets, bordered by lateral ramps, are arrayed in a imbricate fan. These thrust sheets consist of continental-margin stata of Araxá, Canastra and Paranoá Groups. An east to west traverse across this belt passes through Barrovian-type metamorphic facies, from lower greenschist facies in the east to upper amphibolite in the west. Granulite-grade basement slices, derived from the Goiás Central Massif, border the belt at its western edge. The northern limb of the syntaxis consists of a southeast-verging fold-thrust belt. This belt consists of retrograded basement slices interleaved with basement-derived psammitic/pelitic schist. The Goianésia mafic/ultramafic massif borders this belt to the north. Thrust faults parallel to those of the syntaxis's northern limb occur in the southern limb as well, where they cross-cut the east-verging structures of the southern limb. Because the two limbs of the Pirineus Syntaxis have different structural and metamorphic histories, and because structures from the northern limb cross-cut those of the southern limb, I conclude that the two limbs formed during separate, non-coaxial deformation events. This interpretation implies that the Brasilia belt itself form as a result of at least two non-coaxial episodes. These episodes may reflect sequential collision of microcontinents with the western margin of the São Francisco craton during the Neoproterozoic assembly of Gonswana. Subsequent to this history, the region was cut by NW and NE-strike slip faults, perhaps during a late phase of the Brasiliano, and finally by NS-strike Cretaceous dikes.
